Two pressure chambers of the master cylinder and brake cylinders provided respectively for front left and right wheels are respectively connected directly to each other by master passages. Provided respectively in the master passages are master cut-off valves each as a normally-closed electromagnetic open/close valve. As a result, when the brake pedal is not operated and when no current is supplied to solenoids of the respective master cut-off valves, the pressure chambers and the brake cylinders are respectively disconnected to each other, preventing an outflow of the working fluid from the pressure chambers, i.e., fluid chambers of a master reservoir to the brake cylinders.